Hyperon-Induced Inhomogeneous Pion Condensation and Moat Regimes in Neutron Star Cores

TL;DR

This paper analyzes the stability of nuclear matter in neutron star cores, revealing conditions under which inhomogeneous pion condensates and moat regimes emerge, especially with hyperons influencing the equation of state.

Contribution

It provides a stability analysis of pion condensates in nuclear matter, highlighting the role of hyperons in inducing inhomogeneous phases at high densities.

Findings

No instability in beta-equilibrium with only nucleons.

Moat regime appears at high densities with damped oscillatory correlations.

Hyperons can induce instability towards inhomogeneous pion condensates.

Abstract

We perform a stability analysis of the homogeneous ground state of nuclear matter against inhomogeneous perturbations of the pion condensate. In $\beta$-equilibrium, restricting the baryon species to nucleons only, we observe no instability; however, at high densities, the pseudoscalar density-density correlations assume a moat regime, i.e. a damped oscillatory patterned spatial correlation, which in momentum space appears as a non-zero global minimum for some finite three-momentum. When hyperons are permitted to appear, this minimum can cross down to negative values, which configures an instability towards an inhomogeneous pion condensate which ultimately will affect the equation of state.